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Tomorrow crews will begin removing the Seneca Street off-ramp that looms above Seneca Street between the waterfront and First Avenue. Due to its height and proximity to nearby buildings, the contractor Kiewit will use cranes to bring the ramp’s girders down one by one.

Crews will remove the ramp working west to east toward First Avenue. Hoe rams will hammer out the road deck before crews cut the ramp’s girders and beams. Cranes will lift the cut pieces one by one onto the ground. Machinery will munch the girders and the ramp’s columns into rubble. Kiewit used a similar approach when removing the Columbia Street on-ramp in February and March.

Above: Crews lifting a girder from the Columbia Street ramp that had been cut away with saws

Expect detours around Western Avenue and Seneca Street

Kiewit will need to close the intersection of Western Avenue and Seneca Street while removing the ramp above the intersection. Kiewit, WSDOT and SDOT have coordinated closely on the work plan for the ramp’s removal to minimize road closures in the neighborhood. The current closure plan:

Wednesday, May 22: Crews begin site prep and slotting the deck near Alaskan Way.

Thursday, May 23: Crosswalk across Seneca Street at Western Avenue closes at 7 a.m.

Tuesday, May 28: Whole intersection of Seneca Street and Western Avenue closes at 4 a.m., for up to 20 days total.

Saturday, June 1: University Street reopens onto Alaskan Way.

Mid-June: Ramp fully removed, and site restoration begins.

Take note: Between Tuesday and Saturday, May 28 – June 1, Western Avenue will be a dead-end street south of Virginia Street. Businesses and sidewalks will be open north and south of Seneca Street, but people walking, biking and driving will need to find alternate paths to cross Seneca Street. See the map below:

When University Street reopens on June 1, it will be a connection point between the waterfront and Western Avenue. The intersection of Post Avenue and Seneca Street will also close for up to seven days in late May or early June as crews remove the ramp overhead.

What to expect from the work

The contractor’s current plan calls for the ramp to be removed in about three weeks, with crews working only during daytime hours. Buildings adjacent to the work will be protected in the air by nets hung from cranes, and on the ground by barriers. Work hours could change based on crews’ progress, but the planned work hours are:

7 a.m. – 8 p.m. weekdays

9 a.m. – 8 p.m. Saturdays

9 a.m. – 5 p.m. Sundays

The work will unavoidably produce noise, dust and vibration, but crews will work to mitigate those effects where possible. The process for removing this ramp is benefitting from crews’ experience working on earlier sections of the viaduct, and Kiewit has refined their methods since the project began.

Follow up work at First Avenue in June

After the ramp is removed, crews will need to conduct follow-up utility work where the ramp once met First Avenue. Crews will also restore the sidewalk on the west side of First Avenue and build a wall and rail in the hole where the ramp once stood. This work has not yet been scheduled, and may involve night work. We will post more details about this work on our website once the plan is confirmed.

Every day trucks carry viaduct rubble south to Terminal 25 along the Duwamish River for processing. There, rebar is removed, and the concrete crushed into small pieces. The processed rubble is then trucked up to Battery Street to fill the tunnel.

Filling the Battery Street Tunnel from the surface has begun

Work to decommission the aged and seismically vulnerable Battery Street Tunnel continues as crews fill the tunnel from the surface level. Trucks pour processed viaduct concrete rubble into a hopper (a sort of funnel) placed atop the Battery Street Tunnel’s old ventilation grates. The hopper contains water sprayers and rotates as it pours its contents into the tunnel to prevent dust. Inside the tunnel, the rubble falls into piles which crews spread and then compact with a vibratory roller. The fill material will be placed and compacted up to about seven feet from the ceiling.

What’s ahead

Placing the crushed concrete will last about three months. The final seven feet of the tunnel’s interior will be filled with a low-density cellular concrete; this work is scheduled to occur in late 2019 and early 2020. See our earlier post for details about work hours.

Once the tunnel is filled, the vents will be removed and sealed up as part of other surface street restoration work on Battery Street scheduled for summer 2020.

Work is progressing on the three blocks of Seventh Avenue North in the South Lake Union neighborhood between Denny Way and Harrison Street. (This stretch of road used to be called Aurora Avenue North.) The North Surface Streets Project will turn what had been highway ramps and the sunken approach to the Battery Street Tunnel into a surface street with north/south bus lanes and signalized intersections at John and Thomas streets.

The project is phased to keep vehicles moving on Seventh Avenue North during construction. Next week the work zones will shift to accommodate new areas of construction. These lane configurations will be in place 24/7 for about four weeks. Here are the changes coming May 13 – 14:

Lane Shift: Beginning Tuesday, the northbound lane of Seventh Avenue North between John and Harrison streets will be shifted onto new concrete. No turn movements will be affected.

Lane reduction: Beginning Tuesday, Seventh Avenue North will be reduced to one northbound lane north of Denny Way.

Borealis Avenue narrowed: Borealis Avenue will be tapered down to one lane to accommodate Battery Street Tunnel filling operations and to align traffic with the single lane of Seventh Avenue North that begins north of Denny. The taper will change sides of the street depending on what work activity is being performed. The bus stop will remain open.

Removing the left lane north of Denny Way will give crews space to dismantle and fill the Battery Street Tunnel’s portal and raise the trench to ground level. Shifting the travel lane at John Street will provide space to work on Seventh Avenue North’s future outside lane between John and Harrison streets. See the map at right (click for larger version).

Future work

Later this month, Denny Way will be reduced to one lane in each direction for overnight utility work beneath the street. Later this summer, the contractor will move into the next major phase of the North Surface Streets Project, when Seventh Avenue North's travel lanes in both directions will be shifted into the center of the road so crews can work on the outside lanes.

Crews have already cleaned the tunnel of decades’ worth of automobile exhaust and removed the tunnel’s mechanical and electrical systems. They will continue to install sewer lines and conduct other utility work. But starting as soon as next week, the contractor will begin trucking in concrete rubble from the viaduct demolition and sending it into the tunnel using funnels on Battery Street. Crews removed steel rebar from the rubble and crushed the concrete into baseball-sized pieces.

Caption: The ledge at left is fill material already brought in by truck and compacted to support a new sewer line that will be placed on top. The yellow chute at right is part of the tunnel ventilation system to keep fresh air circulating for workers.

Inside the tunnel, crews will compact the fill using a vibratory roller. The work will last at least three months as crews fill up to about seven feet from the top of the tunnel.

Effects of construction

One lane or sidewalk at a time will be closed on Battery Street between First Avenue and Sixth Avenue, depending on where crews are filling on a given day. The compaction happening inside the tunnel causes vibrations that may be felt on the surface and in adjacent buildings.

Funnels and other construction equipment stored on Battery Street when not in use.

People living, working or traveling near the work may see and feel increased noise, dust and vibration during the work hours (weekdays 6:30 a.m. – 5:30 p.m.). The filling operation ends at 3 p.m. to keep Battery Street fully open during the evening commute.

Caption: Side-dumping trucks like the one above will deposit fill into funnels on Battery Street.